This invention relates generally to the field of postage meters for mailing machines, and more particularly to an improved printing mechanism for pressing a mail piece against a postage indicia printing die in a high speed flat bed type printer.
Automated mail processing apparatus is well known and widely used in large volume mailing applications where a high throughput speed is essential. Some examples of large volume mailing in the context of the aforementioned apparatus are credit card companies, banks, chain department stores, book clubs, etc., where each month some form of mailing, such as bills, solicitations, advertisements, etc., are sent to tens if not hundreds of thousands of card holders, customers, subscribers, etc., as the case may be. Were it not for the type of mail processing apparatus with which the present invention is concerned, such mass mailings could not be carried out.
This type of mail processing apparatus generally comprises a plurality of mail processing components disposed adjacent one another and defining a feed path along which individual mail pieces are fed seriatim from one component to another. In a typical installation, mail, which has already been assembled by suitable collating and envelope inserting equipment, is either fed directly to the mail processing apparatus, or may be manually stacked in the hopper of a separator/feeder component of the mail processing apparatus which feeds the mail pieces into an envelope flap sealer component where the flaps are moistened, folded over and sealed. The mail pieces are then fed onto the platform of a weighing component which weighs each piece, either to ensure that it's weight is within preset limits for the application of a preset amount of postage, or to change the postage amount printing wheels of a postage meter component to cause it to print a different amount of postage. The mail pieces are then either in position to have postage printed thereon, or are fed to such position, depending upon the size of the mail pieces, after which an appropriate amount of postage is printed on the mail pieces.
In mail processing apparatus of the apparent degree of sophistication, complexity and cost as that just described, it is essential that such equipment operate at a high rate of speed in order to achieve maximum efficiency and make the apparatus cost effective. Much of the mail processing apparatus now in commercial use has achieved this objective and operates relatively successfully. Certain problems do exist, however, some more serious than others, and continuing design and development is carried on generally to constantly improve the performance of the apparatus and particularly to find solutions to problems which have become known.
One problem in particular that is of major significance in mail processing apparatus is the print quality of the postage indicia printed on the mail pieces by the printing mechanism of the postage meter. In order for postage meters to be accepted for commercial use by the United States Postal Service, the printing mechanism of the meters must be able to print postage indicia which meets certain standards of print quality established by the USPS. Since the postage indicia contains certain vital information, such as the location from which mail is dispatched, the date thereof and the amount of postage paid by the sender, it is necessary that the indicia be printed with sufficient clarity that this information can be readily read when necessary. Postage indicia which is not readable is unacceptable to the USPS, and postage meter equipment which prints such indicia will not be approved for commercial use.
A major factor which contributes to poor postage indicia print quality is the speed of operation of the postage meter printing the indicia. A postage meter that prints a perfectly acceptable indicia at one speed may not print an acceptable indicia when operated at a considerably higher speed. This is particularly so in the case of a postage meter printing device having a flat bed printer, i.e., a printer having a fixed flat postage indicia printing die against which a mail piece is pressed by a movable platen. The dynamic forces involved in bringing the ink receiving surface of mail pieces into intimate contact with the inked surface of the printing die are much more complicated in the case of the flat bed printer than they are with a curved printing die in a rotary printer where printing of the indicia takes place while the mail pieces are in motion.
In existing automated mail processing apparatus as previously described, the weighing component comprises a scale having a platform which forms a segment of the feed path along which mail pieces are fed. A transport mechanism, comprising generally a plurality of transport rollers, or an endless transport belt, in cooperation with opposed pressure skis which include rollers which press the mail piece into firm engagement with the transport rollers or belt, moves each mail piece onto the platform and stops the movement when the mail piece is in a desired position for weighing. The postage meter is generally situated behind the platform of the weighing scale in a position such that, depending on the size of the mail piece, it will be in position for printing of the postage indicia by the postage meter when it is in the weighing position. This is true at least for most standard and large size mail pieces; short mail pieces may have to be further advanced along the scale platform to bring them to a desired printing position. After a mail piece is weighed, a rigid platen having a resilient pressure pad affixed to the upper surface thereof rises from below the level of the upper surface of the scale platform and pushes upwardly on the upper right hand corner of the mail piece to bring it into intimate contact with the underside of the printing die, which is inked just prior to each printing operation by a suitable inking device that is part of the printing mechanism of the postage meter. During the time that the corner of the mail piece is being moved upwardly by the platen, the rest of the mail piece remains captured between the transport rollers or belt and the pressure skis to prevent inadvertent movement of the mail piece.
The dynamic problem that occurs during this operation of the printing mechanism at a high rate of speed is that when the platen rises, the upper surface of the pressure pad makes initial contact with the undersurface of the mail piece adjacent a corner of the mail piece where the postage indicia is to be printed, and allows it to tilt with respect to the top of the pressure pad. As the image area portion of the mail piece tilts, the plane of at least this portion of the mail piece, and perhaps its entirety, is disposed at an angle to the plane of the upper surface of the pressure pad and also the lower surface of the printing die, these two surfaces being parallel to one another. As the platen continues to rise, the lower surface of the image area portion of the mail piece is clamped by the skis against the pressure pad so that only the forward upper edge of the pressure pad contacts the lower surface of the mail piece, with the result that a pivot line is established in the mail piece adjacent the outboard edge of the pressure pad. As the pressure pad pushes further upwardly on the now angled portion of the mail piece, it lifts the skis and raises the image area portion of the mail piece to contact the printing die at the angle described. However, during this further upward movement, the rear edge of the mail piece makes initial contact with the printing die adjacent the rear edge thereof, thereby establishing an initial contact at the rear edge of the mail piece and producing an image of a rear portion of the printing die. Since the image area portion of the mail piece is rigidly held between the upper forward edge of the pressure pad and the ski or skis being pushed upwardly thereby, and since the pivot line can only rise vertically, the upward movement of the pressure pad, which is causing the image area portion to gradually become parallel to the under surface of the printing die, causes the rear edge of the mail piece to shift laterally a slight amount with respect to the surface of the printing die, with the result that the entire image area portion of the mail piece is displaced slightly with respect to the surface of the printing die while it is being pressed into intimate contact with the surface of the printing die. This relative movement, slight as it may be, between the image area portion of the mail piece and the surface of the printing die, is sufficient to cause ink to smudge or smear and result in a printed indicia which lacks the quality of clarity required by the USPS standards for acceptable postage indicia printing.